The present application relates to a Thin Film Transistor (TFT) used in a display device or the like, and a method of manufacturing the same.
In recent years, with a view to application of a Thin Film Transistor (TFT), a light emitting device, a transparent conductive film, and the like to electronic apparatuses, the research and development of oxide semiconductors such as a zinc oxide and an indium gallium zinc oxide are very active. It is found out that when the oxide semiconductor is used in an active layer (channel) of the TFT, the oxide semiconductor shows a high electron mobility, and thus shows excellent electrical characteristics as compared with the TFT using amorphous silicon. In addition, the oxide semiconductor has an advantage such that even at a low temperature close to a room temperature, the high mobility can be expected, and so forth, and thus the positive development of the oxide semiconductor is progressed. With regard to the TFT using such an oxide semiconductor layer, a bottom gate type structure, and a top gate type structure have been reported. The bottom gate type structure, and the top gate type structure, for example, are described in PCT Patent Publication No. WO 2005-088726 and Japanese Patent Laid-Open No. 2007-194594.
However, in the oxide semiconductor, a film quality is easy to deteriorate due to breakaway of oxygen, mixing of hydrogen, and the like. This results in that in the TFT, a threshold voltage is shifted to a minus side, the current-voltage characteristics and the like are deteriorated, and so forth.
In order to cope with such a situation, a technique for forming a protective film made of an aluminum oxide (Al2O3) or the like as a protective film for an oxide semiconductor layer becoming a channel has been proposed. This technique, for example, is described in Japanese Patent Laid-Open No. 2010-135462. Such a protective film, for example, can be deposited in an atmospheric ambient of a mixed gas of oxygen (O2) and argon (Ar) with aluminum as a target by, for example, utilizing a reactive sputtering method.